sPHENIX discussion of physics

["Perepelitsa, Dennis" <dvp AT bnl.gov>]

Hi Tony and all,

We discussed this in our JS TG report in the 13 November General Meeting, see slide 4 here: https://indico.bnl.gov/event/10081/contributions/43523/attachments/31369/49520/dvp-sPHENIX-GM-11-13-20.pdf . 

Since the MBD and EPD have been recently put into GEANT, we (in the JS TG) think it is high time to try to use centrality observables similar to how we would in real data. 

Additionally, I think it is better to separate the centrality-measuring region from the central region where we will do the physics measurements, rather than using a centrality observable at mid-rapidity like the total number of tracks or hits. This helps avoid auto-correlations which, although they may not play a big role in central events, certainly will in peripheral AA events and in p+A.

Our proposal was to headquarter this effort in the JS TG. Practically, this would mean that all TGs should include the MBD (and possibly the EPD) in their simulation & reconstruction macros. We would provide a prescription for how to form centrality observables (i.e. might be slightly non-trivial in the EPD due to the needed Landau tail suppression), and then deliver cuts derived from MB Hijing events to the other TGs.

This proposal got a positive response in real time during the meeting, but we’re happy to discuss in more detail.

Dennis

On Nov 23, 2020, at 2:19 PM, Anthony Frawley <afrawley AT fsu.edu> wrote:

Hi All,

I would like to understand how the topical groups plan to make centrality selections when analyzing the MDC data. 

What are people planning to do?

One could use the vertex object associated with each collision. The existing code (PHVertexFinder) will create a vertex object for each collision vertex and place it on the node tree in SvtxvertexMapActs. Each collision vertex will have a list of track keys associated with that vertex. That list can be used to access the tracks from SvtxTrackMap. The most basic centrality selection could be just the number of tracks associated with the collision vertex. More advanced selections could involve applying cuts on the associated tracks. 

Cheers

Tony

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Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder